Tar sand occurs on a very large scale in nature, for instance in Canada, Venezuela, the United States, Russia and Rumania. It contains about 10%w of heavy hydrocarbon oil which may be obtained from it by extraction. This "tar sand oil" has a high viscosity and a high content of oxygen, sulphur and metal compounds, especially vanadium and nickel compounds.
In view of the increasing demand for crude petroleum oil and the strongly increased price thereof, there is a great interest in processes which offer the possibility to convert, in an economically acceptable way, heavy hydrocarbon oils such as tar sand oils into hydrocarbon mixtures of which the boiling point distribution shows much resemblance to that of crude petroleum oil. Such hydrocarbon mixtures will be further referred to herein as "synthetic crude oils".
Since the boiling point distribution of tar sand oil shows some resemblance to that of an atmospheric distillation residue of a crude petroleum oil, investigation has first focused on the extent known processes for the preparation of synthetic crude oil from atmospheric distillation residues of crude petroleum oil are suitable for application to tar sand oil. In view of the high metal content of tar sand oil, the investigation was first concentrated on a process which yielded excellent results in the preparation of synthetic crude oil from an atmospheric distillation residue of a crude petroleum oil having a high metal content. In this process, the atmospheric distillation residue is first separated by vacuum distillation into a vacuum distillate and a vacuum residue. The vacuum residue is subsequently separated by deasphalting into a deasphalted oil and asphalt. Finally, the vacuum distillate and the deasphalted oil are blended and from the mixture a synthetic crude oil is prepared by subjecting the mixture successively to catalytic hydrodemetallization and catalytic hydrocracking. Application of the above-described process, which will further be referred to as the "standard conversion process", to a tar sand oil instead of to an atmospheric distillation residue of a crude petroleum oil, yields a synthetic crude oil. However, the results are insufficient on certain points. Deficiencies include the yield of C.sub.5.sup.+ product, the hydrogen consumption, the stability of the hydrocracking operation and the sulphur content, and the viscosity and the boiling point distribution of the 180.degree. C..sup.+ product.
Continued investigation into the preparation of synthetic crude oil from tar sand oil has shown that a much more attractive result can be obtained if certain deviations from the standard conversion process are made. Instead of a mixture of the vacuum distillate and the deasphalted oil being subjected to a hydrogen treatment, the two oils are hydrotreated separately. The vacuum distillate is catalytically hydrocracked without previous demetallization. The deasphalted oil is not cracked but is first catalytically hydrodemetallized and thereafter catalytically hydrodesulphurized.
If the results obtained with the process now proposed are compared with those of the standard conversion process, it appears that the process now proposed
(a) gives a higher yield of C.sub.5.sup.+ product, PA1 (b) consumes less hydrogen, PA1 (c) shows a more stable hydrocracking operation, and PA1 (d) gives a 180.degree. C..sup.+ product with a lower viscosity and sulphur content as well as a more attractive boiling point distribution.